A vehicle steering apparatus is structured as shown in FIG. 7. The movement of a steering wheel 1 to be operated by a driver is transmitted to an input shaft 6 of a steering gear unit 5 through a steering shaft 2, a universal joint 3, an intermediate shaft 4 and another universal joint 3. And, a pair of right and left tie rods 7, 7 are pushed and pulled by a rack and opinion mechanism built in the steering gear unit 5 to thereby apply proper steering angles to a pair of right and left steering wheels according to the operation amount of the steering wheel 1. Here, as the intermediate shaft 4, generally, there is used a shaft structured such that, as shown in FIG. 8, the one-side ends of an outer shaft 8 and an inner shaft 9 are serration engaged with each other to thereby enable torque transmission and contraction in a collision accident. The universal joints 3, 3 are connected to the other-side ends of the shafts 8, 9.
As the universal joints 3, 3 to be incorporated into the steering apparatus, there are used, for example, such cross shaft universal joints as disclosed in the patent document 1. Description is given of a conventional structure of one of yokes constituting such cross shaft universal joints and including a basic structure to be aimed at by the invention with reference to FIGS. 9 to 11E. A yoke 10 of the conventional structure is a so called press yoke which is formed by punching and bending sequentially a metal plate such as steel material using a press, and includes a base part 11 and a pair of connecting arm parts 12, 12.
The base part 11 has a partially-lacking cylindrical shape and includes a discontinuous portion (slit) 13 for enabling expansion and compression of the inside diameter of the base part 11 in one circumferential location thereof. It also includes first and second flange portions 14, 15 while they are sandwiching the discontinuous portion 13 from both sides in the circumferential direction thereof. It further includes a female serration 16 in the inner peripheral surface thereof. Also, because a metal plate is folded back, the first and second flange portions 14, 15 have a double thickness dimension of a metal plate. The first and second flange portions 14, 15 have a through hole 17 and a screw hole 18 at the mutually matching positions of the first and second flange portions 14, 15 while the through hole 17 and the screw hole 18 are respectively twisted with respect to the axis of the base part 11. Also, in the free state of the yoke 10, the first and second flange portions 14, 15 are substantially parallel to each other, while the through hole 17 and screw hole 18 are arranged concentrically with each other.
The connecting arm parts 12, 12 extend in the axial direction from such two locations of the one axial end edge (in FIG. 9, upper end edge) of the base part 11 as are opposed to each other in the diameter direction of the base part 11. Also, the arrangement direction (in FIGS. 9 and 10, right and left direction) of the connecting arm parts 12, 12 is circumferentially coincident (parallel to) with the arrangement direction (in FIG. 10, right and left direction) of the first and second flange portions 14, 15. And, the connecting arm parts 12, 12 include mutually concentric circular holes 19, 19 in their respective tip portions.
As shown in FIG. 11A, the yoke 10 having the above structure is made of a flat material plate 22 which includes a base plate part 20 and a pair of tongue-like parts 21, 21. Firstly, the two ends of the base plate part 20 of this material plate 22 are respectively folded back 180° in their respective middle portions, thereby providing a first intermediate material 23 as shown in FIG. 11B. Next, the first intermediate material 23 is pressed between a pair of extrusion molding dies to be deformed plastically, thereby providing a second intermediate material 24 as shown in FIG. 11C. In the second intermediate material 24, the tongue-like parts 21, 21 to provide the pair of connecting arm parts 12, 12 are curved in a partially cylindrical manner, the base end near portions of the tongue-like parts 21, 21 are bent substantially in a crank shape, and the intermediate portions of the tongue-like parts 21, 21 to the tip end near portions thereof are offset with respect to the base plate part 20. Next, of the thus-structured second intermediate material 24, the central portion of the base plate part 20 is slightly curved to provide a third intermediate material 25 as shown in FIG. 11D. Next, the base plate part 20 of the third intermediate material 25 is curved further to provide a fourth intermediate material 26 as shown in FIG. 11E. In this state, there are formed the base part 11 and the pair of connecting arm parts 12, 12 to be equipped in the yoke 10 after completed. Finally, the through hole 17 and screw hole 18 are formed in the first, second flange portions 14, 15 constituting the base part 11, the female serration 16 is formed in the inner peripheral surface of the base part 11, and the circular holes 19, 19 are formed in the connecting arm parts 12, 12, thereby providing the yoke 10 as shown in FIGS. 9 and 10.
As shown in FIGS. 12 to 14, to assemble a cross shaft universal joint using the above-produced yoke 10, inside the circular holes 19, 19 formed in the tip portions of the connecting arm parts 12, 12, there are pivotally supported the two ends of one shaft part 28a of a pair of shaft parts 28a, 28b constituting a cross shaft 27. Thus, cup bearings 29, 29 are internally engaged with and fixed to the insides of the circular holes 19, 19.
The cup bearings 29, 29 respectively correspond to shell-type needle bearings and include bottomed cylindrical cups 30, 30 corresponding to shell-type outer rings, and multiple needles 31, 31. And, while the cups 30, 30 are pressure inserted into the circular holes 19, 19, the two ends of one shaft part 28a constituting the cross shaft 27 are respectively inserted into the radial-direction insides of the needles 31, 31. Thus, the two ends of the shaft part 28a are rotatably supported on the yoke 10.
Also, for assembling a steering apparatus, to connect and fix the base part 11 of the yoke 10 to the end of a rotation shaft constituted of any one of the steering shaft 2, intermediate shaft 4 and input shaft (see FIG. 7) in a torque transmittable manner, firstly, the end of the rotation shaft is inserted into the inside of the center hole (serration hole) of the base part 11, in the free state of the yoke 10. Thus, the female serration 16 formed in the inner peripheral surface of the base part 11 is serration engaged with a male serration formed in the outer peripheral surface of the end of the rotation shaft. Next, as shown in FIGS. 12 and 13, a bolt 32 is inserted into the through hole 17 and is threadedly engaged with the screw hole 18, and is further tightened. Thus, the width of the discontinuous part 13 is elastically narrowed, thereby reducing the diameter of the base part 11 elastically. As a result, the surface pressure of the serration engaged part increases, whereby the base end 11 is connected and fixed to the end of the rotation shaft in a torque transmittable manner.
In the yoke 10 having the above structure, for reason of securing the assembling workability of the cup bearings 29, 29, the end of the shaft part 28a constituting the cross shaft 27 is inserted into the radial-direction insides of the needles 31, 31 constituting the cup bearings 29, 29 with a certain degree of clearance. Therefore, when in use, there is a possibility that the end of the shaft part 28a can shake in the diameter direction (radial direction) relative to the cup bearings 29, 29 and can generate strange sounds. Also, such shaking motion can probably become excessively large with long use.
In view of the above circumstances, for example, the patent document 2 discloses an invention in which the peripheral part of a circular hole of a connecting arm part, constituting a yoke, with a cup bearing being pressure inserted therein is plastically deformed to thereby suppress occurrence of shaking motion between the cup bearing and the shaft part of a cross shaft. Also, for example, the patent document 3 discloses an invention in which the shape of a cup constituting a cup bearing is worked (the cylindrical part thereof is deformed) to thereby suppress occurrence of shaking motion between the cup bearing and the shaft part of a cross shaft. However, in both of the inventions of the patent documents 2 and 3, for suppression of occurrence of shaking motion, exclusive working on the connecting arm part or cup is necessary. This inevitably increases the working cost of the cross shaft universal joint.
Here, in the conventional structure shown in FIGS. 9 to 14, the circumferential phases of the arrangement direction of the pair of connecting arm parts 12, 12 and the arrangement direction of the first, second flanges 14, 15 are identical with each other. Thus, even when the first, second flanges 14, 15 are deformed in their mutually approaching directions by tightening the bolt 32, as shown by a thick arrow in FIG. 14, the connecting arm parts 12, 12 are simply flexually deformed in the mutually approaching directions in the axial direction of the circular holes 19, 19 which is a direction parallel to the arrangement direction of the first, second flange portions 14, 15; that is, there does not occur such deformation as can reduce the above-mentioned shaking motion.